Field Guide/Mammals/Muskrat

Size: The average length of the Muskrat is 15.75-27.5 inches (40- 70 cm) long, almost half of that makes up their tail. It weights between 2- 4 lbs (908-1816 g). [1]Muskrats are much larger than the other animals in their subfamily, which include the vole and the lemming.

Description: The Muskrat is a medium-sized semiaquatic rodent that is native to North America. They are covered with short, dense fur, which is medium to dark brown or black in color, with a lighter underside. As the muskrat ages, it turns partly gray in color. The fur has two layers, which helps protect them from the cold water. To aid them in swimming, they have a long tail covered with scales rather than hair, and are slightly flattened from side to side which is a shape that is unique to them. [1]

Similar Species: The muskrat is the only species in genus Ondatra, but it is the largest species in the subfamily Arvicolinae, which includes 142 other species of rodents, mostly voles and lemmings. The muskrat’s distinguishing features from these other species is it’s overall coloration, it’s waterproof fur with chestnut to hazel sides and underbelly, it’s tail flattened vertically, and it’s furless hind feet that are partially webbed.[2]

Range: Muskrats are found over most of the United States and Canada and a small part of northern Mexico. They were also introduced to Europe in the beginning of the 20th century.

Habitat: Muskrats mostly inhabit wetlands, areas in or near saline and freshwater wetlands, rivers, lakes, or ponds. They are able to live alongside streams and slow-moving rivers and in waters that are deep enough not freeze at the bottom. [2]

Diet: The muskrat commonly eats the cattail, yellow water lily, and other aquatic vegetation. They do not store food for the winter, but sometimes eat the insides of their lodges. Plant materials make up 95% of their diet, and they also eat small animals such as freshwater mussels, frogs, crayfish, fish, and small turtles. [3]

Activity: Muskrats are most active at night or near dawn and dusk. Muskrats follow trails they make in swamps and ponds, and when the water freezes, they continue to follow their trails under ice. They normally live in groups consisting of a male and female and their young. In the spring, they often fight with other muskrats over territory and potential mates.

Reproduction: During the spring, muskrats often fight with each other over territory and potential mates. Many are injured or killed in these fights. Muskrat families build nests to protect themselves and their young from cold and predators. They are prolific breeders, where the females can have two to three litters a year of six to eight young each. Babies are born small and hairless, and weigh only about 22 grams. Young muskrats mature between 6 months to a year. The gestation period for muskrats is 22-30 days. [1]

Notes: The muskrats are sometimes referred to as “rats” in a general sense because they are medium-sized rodents with an adaptable lifestyle and omnivorous diet, but they are not, however, “true rats” because they do not belong in the genus Rattus.

American Indians have long considered the muskrat to be a very important animal. Some predict winter snowfall levels by observing the size and timing of muskrat lodge construction. Contrary to belief, though, the thickness of muskrat lodges does not indicate the severity of the coming winter. The muskrat’s underfur traps air, and prevents the skin of the muskrat from becoming wet while it is in the water. Musk glands are predominant beneath the skin on the lower abdomen of male muskrats. These two glands become swollen during the spring and produce a yellowish, musky smelling fluid. Thus, the name “muskrat”. With their webbed feet, muskrats can also swim at a speed up to 3 miles per hour and can even swim backwards. [5]

Unlike the beaver, the muskrat does not store food for the winter. It needs to eat fresh plants each day, and sometimes it makes channels in the mud to get from its house to reach food under the ice. To stay warm in winter, groups of muskrats huddle together in their lodges.Muskrats have the ability to hold their breath underwater for a 12-17 minutes while searching for food. When food is scarce, female muskrats have been known to eat their young. [6]